1. Field of the Invention
The present invention relates to a semiconductor light emitting apparatus and a method for producing the same.
2. Description of the Related Art
Usually in a semiconductor laser device used as a light source for an optical disc apparatus, a semiconductor laser device is die-bonded to a metal layer on a sub mount.
FIG. 9A is a schematic cross-sectional view of a conventional semiconductor laser apparatus 100, and FIG. 9B is a schematic plan view thereof.
In the semiconductor laser apparatus 100, a pair of metal layers 123 including a metal layer 123A and a metal layer 123B are provided on a surface of a rectangular parallelepiped sub mount 122 formed of a non-conductive material. A semiconductor laser device 121 is die-bonded to the metal layer 123A and the metal layer 123B respectively by a solder material member 124A and a max material member 124B.
The metal layers 123A and 123B have a similar rectangular shape, and are electrically separated from each other by a separation area 129 linearly defined on a central area of a surface of the sub mount 122. The separation area 129 has a prescribed width. The metal layers 123A and 123B cover the entire surface of the sub mount 122 except for the separation area 129. In the separation area 129, the surface of the sub mount 122 is exposed.
A solder material attachment area 123a is a rectangular area extending in a longitudinal direction of the metal layer 123A from one end of the metal layer 123A. The solder material attachment area 123a is also adjacent to the separation area 129. To the solder material attachment area 123a, the solder material member 124A is attached. A solder material attachment area 123b is a rectangular area extending in a longitudinal direction of the metal layer 123B from one end of the metal layer 123B. The solder material attachment area 123b is also adjacent to the separation area 129. To the solder material attachment area 123b, the solder material member 124B is attached. The solder material attachment area 123a and the solder material attachment area 123b are located to face each other with the separation area 129 interposed therebetween.
The semiconductor laser device 121 is bridged over the separation area 129 at one end portion thereof in the longitudinal direction, and is located above the metal layers 123A and 123B.
The semiconductor laser device 121 includes a semiconductor layer (not shown) provided on a substrate (not shown), two light emitting points 121a and 121b in an upper portion of the semiconductor layer, and an electrode (not shown) above each of the light emitting points 121a and 121b. The electrodes are provided for applying a supply voltage. Then, the semiconductor laser device 121 is positioned such that the electrode above the light emitting point 121a and the electrode above the light emitting point 121b respectively contact the solder material members 124A and 124B, and such that the substrate of the semiconductor laser device 121 is located in an upper portion of the semiconductor laser apparatus 100. The substrate of the semiconductor laser device 121 is provided with an electrode (not shown) for applying aground voltage.
To the electrode provided to the substrate of the semiconductor laser device 121, a wire (not shown) which is electrically connected to the ground (ground voltage) is wire-bonded. To each of the metal layers 123A and 123B, a wire (not shown) electrically connected to the supply voltage is wire-bonded.
The solder material member 124A is located on the rectangular solder material attachment area 123a of the metal layer 123A along the separation area 129, and the solder material member 124B is located on the rectangular solder material attachment area 123b of the metal layer 123B along the separation area 129. A total area of the solder material attachment areas 123a and 123b is larger than a die-bond area of the semiconductor laser device 121 (i.e., a total area of the bottom surface of the semiconductor laser device 121 facing the solder material attachment areas 123a and 123b).
The semiconductor laser device 121 is die-bonded in the following manner.
The solder material member 124A is located on the solder material attachment area 123a of the metal layer 123A, and the solder material member 124B is located on the solder material attachment area 123b of the metal layer 123B. Next, the semiconductor laser device 121 is located on the solder material members 124A and 124B. Then, the solder material members 124A and 124B are heated to be melted, and the semiconductor laser device 121 is die-bonded to the metal layers 123A and 123B by the melted solder material members 124A and 124B.
The semiconductor laser apparatus 100 is required to cause the semiconductor laser device 121 to stably operate even at a very high temperature. In order to realize this, it is necessary to efficiently diffuse heat by the sub mount 122. This can be realized by increasing the amount of the solder material of the solder material members 124A and 124B to improve the adhesiveness between the semiconductor laser device 121 and the sub mount 122, and thus to reduce the heat resistance between the semiconductor laser device 121 and the sub mount 122.
However, when the amount of solder material of the solder material members 124A and 124B is increased, the state shown in FIGS. 10A and 10B occurs. More specifically, when the semiconductor laser device 121 is die-bonded to the metal layers 123A and 123B, the melted solder material members (represented by reference numeral 124A′ and 124B′) flow to the vicinity of the solder material attachment areas 123a and 123b. As a result, a large area of the surface of the metal layers 123A and 123B is covered with the melted solder material members 124A′ and 124B′. When this occurs, the area of the metal layers 123A and 123B bonded to the wires is reduced, which makes the wire-bonding work difficult.
The semiconductor laser apparatus 100 is picked up using a collet having a recess in which the semiconductor laser device 121 can fit.
For picking up the semiconductor laser apparatus 100 using such a collet, the collet needs to adhere to a surface of the metal layers 123A and 123B. Where a large area of the metal layers 123A and 123B is covered with the melted solder material members 124A′ and 124B′ as shown in FIGS. 10A and 10B, the collet cannot adhere to the surface of the metal layers 123A and 123B. In this case, the semiconductor laser apparatus 100 may not be picked up.
Japanese Laid-Open Publication No. 4-186688 discloses a semiconductor laser apparatus in which the sub mount is formed of a material having no wettability with respect to the melt-adhesion metal (for example, the solder material) except for an melt-adhesion area of the die-bond surface of the sub mount. Thus, the melt-adhesion area does not protrude from the die-bond surface of the semiconductor laser chip (semiconductor laser device).
Japanese Laid-Open Publication No. 11-284098 discloses a semiconductor laser apparatus in which the area to which the solder material is to adhere is smaller than the die-bond area of the laser chip and the sub mount. Thus, the solder material does not protrude from the die-bond surface of the laser chip.
In the semiconductor laser apparatuses disclosed in Japanese Laid-Open Publications Nos. 4-186688 and 11-284098, the solder material is provided so as not to protrude from the die-bond area of the semiconductor laser device. However, when the area in which the solder material is provided is smaller than the die-bond area, the amount of the solder material cannot be increased, and thus the heat resistance between the semiconductor laser device and the sub mount cannot be reduced. As a result, the semiconductor laser device cannot be operated at a high temperature.
Japanese Laid-Open Publication No. 11-284098 discloses a structure in which a groove is provided so as to surround the area to which the solder material is to adhere, inner to the outer perimeter of the laser chip. In this case also, the area for the solder material is limited to the inside of the die-bond area of the laser chip. Therefore, the amount of the solder material cannot be increased, and the laser chip cannot be stably operated at a high temperature.